Semiconductor device and method of forming the same

ABSTRACT

A semiconductor device includes a substrate, a metal gate and a poly gate. The substrate includes a first region and a second region. The metal gate is disposed on the first region of the substrate. The poly gate is disposed on the second region of the substrate. A gate area of the poly gate is greater than that of the metal gate.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. In the course of IC evolution, high voltage technology has been widely used in power management, regulators, battery protectors, DC motors, automotive circuits, panel display drivers, etc. On the other hand, low voltage technology is typically used for logic cores, microprocessors, and microcontrollers. Some modern IC designs integrate both high voltage and low voltage devices on a single chip. The gate area of the high voltage devices is usually larger than that of the low voltage devices. The larger gate area of the high voltage devices results in dishing issue during the successive Chemical Mechanical Polishing (CMP) processes.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIGS. 1 through 22 are cross-sectional views schematically illustrating a process flow for fabricating a semiconductor device in accordance with some embodiments of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

FIGS. 1 through 22 are cross-sectional views schematically illustrating a process flow for fabricating a semiconductor device in accordance with some embodiments of the present disclosure.

Referring to FIG. 1, a substrate 100 is provided. For example, the substrate 100 may be or may include a semiconductor substrate, such as a bulk semiconductor substrate, a semiconductor-on-insulator (SOI) substrate, or the like. In some embodiments, the substrate 100 includes a semiconductor wafer, such as a silicon wafer. In some other embodiments, the substrate 100 includes an elementary semiconductor substrate such as germanium; a compound semiconductor substrate including silicon carbon, gallium arsenic, gallium phosphide, indium phosphide, indium arsenide, and/or indium antimonide; an alloy semiconductor substrate including SiGe, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP; or combinations thereof. Other semiconductor substrates such as multi-layered or gradient substrates may also be used.

In some embodiments, a pad layer 102 is formed on the substrate 100 and a hard mask material layer 104 is formed on the pad layer 102. The materials of the pad layer 102 and the hard mask material layer 104 may be different. For example, the pad layer 102 may be a silicon oxide (SiOx, x>0) layer and the hard mask material layer 104 may be a silicon nitride (SiNy, y>0) layer. The materials of the pad layer 102 and the hard mask material layer 104 are merely for illustration and the disclosure is not limited thereto.

Referring to FIG. 1 and FIG. 2, a trench isolation fabrication process is performed on the substrate 100 such that isolation structures 106 are formed in the substrate 100 to define active regions. The isolation structures 106 are, for example, shallow trench isolation (STI) structures, or the like. In some embodiments, the trench isolation fabrication process may include the following processes. First, the hard mask material layer 104 may be patterned to form a hard mask layer 104 a. The hard mask layer 104 a may be formed by photolithograph and etching processes. Thereafter, by using the hard mask layer 104 a as an etching mask, the substrate 100 and the pad layer 102 are etched to form trenches. A dielectric material is then deposited to fill the trenches and cover the hard mask layer 104 a. A planarization process, such as a CMP process or an etch-back process is performed to remove the excess dielectric material outside the trenches until the hard mask layer 104 a is exposed, as shown in FIG. 2, thereby forming the isolation structures 106. As such, active regions are defined in the substrate 100 through the isolation structures 106.

In some embodiments, after the isolation structures 106 are formed, a first region 100A and a second region 100B of the semiconductor substrate 100 are defined. In some embodiments, the first region 100A may be a core device region, and the second region 100B may be a high-voltage device region. In some embodiments, the first region 100A is connected to the second region 100B. In some embodiments, the first region 100A is spaced apart from the second region 100B by other regions.

Referring to FIG. 2 and FIG. 3, the hard mask layer 104 a and the pad layer 102 are removed until the semiconductor substrate 100 is exposed. In some embodiments, the removal of the hard mask layer 104 a and the pad layer 102 may be performed by etching processes, such as dry etching, wet etching or a combination thereof. Other suitable removal processes may also be used. In some embodiments, portions of the isolation structures 106 are partially removed such that the top surfaces of the isolation structures 106 and the top surface of the semiconductor substrate 100 are substantially at the same level.

In some embodiments, after the hard mask layer 104 a and the pad layer 102 are removed, a well region 108 a is formed in the first region 100A of the substrate 100, and a well region 108 b is formed in the second region 100B of the substrate 100. The well region 108 a may be p-type well or n-type well, and the well region 108 b may be p-type well or n-type well. For example, when the well region 108 a and/or the well region 108 b are n-type wells, n-type dopants (e.g., phosphorous or arsenic) may be doped into the active regions of the substrate 100 to form the well region 108 a and/or the well region 108 b. Similarly, when the well region 108 a and/or the well region 108 b are p-type wells, p-type dopants (e.g., boron or BF₂) may be doped into the active regions of the substrate 100 to form the well region 108 a and/or the well region 108 b. In some embodiments, the dopant concentrations and/or the depths of the well region 108 a and the well region 108 b may be the same or different. In some embodiments, the dopant concentration of the well region 108 b is less than that of the well region 108 a, and the depth of the well region 108 b is deeper than that of the well region 108 a, but the disclosure is not limited thereto.

In some embodiments, the well region 108 a and the well region 108 b are successively formed in the substrate 100 by implantation processes. For example, a first patterned mask is formed to cover the second region 100B and expose the first region 100A, and a first implantation process is performed on the first region 100A of the substrate 100 to form the well region 108 a. Thereafter, the first patterned mask is removed, and a second patterned mask layer is formed to cover the first region 100A and expose the second region 100B, and a second implantation process is then performed on the second region 100B of the substrate 100 to form the well region 108 b.

Referring to FIG. 3 and FIG. 4, a dielectric material layer 110 is formed on the substrate 100. In some embodiments, the dielectric material layer 110 covers both the first region 100A and the second region 100B of the substrate 100. In some embodiments, the dielectric material layer 110 may be a silicon oxide layer. In some embodiments, the dielectric material layer 110 is formed by a suitable deposition process, such as chemical vapor deposition (CVD), or the like.

Referring to FIG. 4 and FIG. 5, a portion of the dielectric material layer 110 on the first region 100A of the substrate 100 is removed until the top surface of the first region 100A of the substrate 100 is exposed, such that a dielectric layer 100 a is formed on the second region 100B of the substrate 100. In some embodiments, the dielectric layer 100 a covers the second region 100B of the substrate 100, and exposes the first region 100A of the substrate 100. In some embodiments, the dielectric layer 100 a is formed by photolithograph and etching processes.

Referring to FIG. 5 and FIG. 6, an interfacial material layer 111 is formed on the first region 100A of the substrate 100. In some embodiments, the interfacial material layer 111 may be a silicon oxide layer. In some embodiments, the interfacial material layer 111 may be formed by an oxidation process. For example, the interfacial material layer 111 may be formed by oxidizing the exposed portion of the substrate 100 through thermal oxidation or chemical oxidation. Since the second region 100B of the substrate 100 is covered by the dielectric layer 110 a, the interfacial material layer 111 is formed on the first region 100A of the substrate 100, without being formed on the second region 100B of the substrate 100. In some embodiments, the interfacial material layer 111 may be adapted to provide a good interface between the substrate 100 and the subsequently formed high-k dielectric material layer 112 (shown in FIG. 7).

Referring to FIG. 6 and FIG. 7, a high-k dielectric material layer 112, a dummy poly gate material layer 113 and a hard mask material layer 114 are formed over the substrate 100 in sequence by suitable deposition processes, such as CVD, physical vapor deposition (PVD) or the like, or combinations thereof. The high-k dielectric material layer 112 may have a dielectric constant greater than about 4, greater than about 12, greater than about 16, or even greater than about 20. For example, the high-k dielectric material layer 112 may include metal oxide, such as ZrO₂, Gd₂O₃, HfO₂, BaTiO₃, Al₂O₃, LaO₂, TiO₂, Ta₂O₅, Y₂O₃, STO, BTO, BaZrO, HfZrO, HfLaO, HfTaO, HfTiO, a combination thereof, or a suitable material. In some alternative embodiments, the high-k dielectric material layer 112 may optionally include a silicate such as HfSiO, HfSiON LaSiO, AlSiO, a combination thereof, or a suitable material. The dummy poly gate material layer 113 may include polysilicon. The hard mask material layer 114 may include silicon nitride, silicon oxynitride, or the like. In some embodiments, the high-k dielectric material layer 112, the dummy poly gate material layer 113 and the hard mask material layer 114 cover the interfacial material layer 111 and the dielectric layer 110 a.

Referring to FIG. 7 and FIG. 8, the interfacial material layer 111, the high-k dielectric material layer 112, the dummy poly gate material layer 113 and the hard mask material layer 114 are patterned to form an interfacial layer 111 a, a high-k dielectric layer 112 a, a dummy poly gate electrode 113 a and a hard mask layer 114 a stacked in sequence over the first region 100A of the substrate 100. The high-k dielectric layer 112 a is disposed on the interfacial layer 111 a. The dummy poly gate electrode 113 a is disposed on the high-k dielectric layer 112 a. The hard mask layer 114 a is disposed on the dummy poly gate electrode 113 a. The patterning process may include photolithograph and etching processes. After the patterning process of the interfacial material layer 111, the high-k dielectric material layer 112, the dummy poly gate material layer 113 and the hard mask material layer 114, the top surface of the dielectric layer 110 a are exposed.

Referring to FIG. 8 and FIG. 9, a poly gate material layer 115 and a hard mask material layer 116 are formed over the substrate 100 in sequence by suitable deposition processes, such as CVD, PVD or the like, or combinations thereof. The poly gate material layer 115 may include polysilicon. The hard mask material layer 116 may include silicon nitride, silicon oxynitride, or the like. In some embodiments, the poly gate material layer 115 and the hard mask material layer 116 cover the interfacial layer 111 a, the high-k dielectric layer 112 a, the dummy poly gate electrode 113 a, the hard mask layer 114 a and the dielectric layer 110 a.

Referring to FIG. 9 and FIG. 10, the dielectric layer 110 a, the poly gate material layer 115 and the hard mask material layer 116 are patterned to form a gate dielectric layer 110 b, a poly gate electrode 115 a and a hard mask layer 116 a stacked in sequence over the second region 100B of the substrate 100. The poly gate electrode 115 a is disposed on the gate dielectric layer 110 b. The hard mask layer 116 a is disposed on the poly gate electrode 115 a. The patterning process may include photolithograph and etching processes. In some embodiments, the gate dielectric layer 110 b is referred to as a gate oxide layer. After the patterning process of the dielectric layer 110 a, the poly gate material layer 115 and the hard mask material layer 116, the top surface of hard mask layer 114 a is exposed, and sidewalls of the interfacial layer 111 a, the high-k dielectric layer 112 a, the dummy poly gate electrode 113 a and the hard mask layer 114 a are also exposed. In some embodiments, the dummy poly gate electrode 113 a is formed before the poly gate electrode 115 a is formed. However, in some alternative embodiments, the dummy poly gate electrode 113 a may be formed after the poly gate electrode 115 a is formed. The disclosure is not limited thereto.

Referring to FIG. 10 and FIG. 11, spacers 117 a and 117 b are formed. The spacer 117 a is formed on sidewalls of the interfacial layer 111 a, the high-k dielectric layer 112 a, the dummy poly gate electrode 113 a and the hard mask layer 114 a. The spacers 117 b are formed on sidewalls of the gate dielectric layer 110 b, the poly gate electrode 115 a and the hard mask layer 116 a. In some embodiments, a spacer material layer (not shown) is formed over the substrate 100 to cover top surfaces of the hard mask layers 114 a and 116 a and sidewalls of the interfacial layer 111 a, the high-k dielectric layer 112 a, the dummy poly gate electrode 113 a, the hard mask layer 114 a, the gate dielectric layer 110 b, the poly gate electrode 115 a and the hard mask layer 116 a. Thereafter, an etching process, such as etching back process, may be performed to remove horizontal portions of the spacer material layer, thereby forming the spacers 117 a and 117 b. In some embodiments, materials of the spacers 117 a, 117 b and materials of the hard mask layers 114 a, 116 a may be different or the same. In some embodiments, materials of the spacers 117 a, 117 b include silicon oxide, silicon nitride, or the like.

In some embodiments, one or more implantation processes may be performed to form source/drain (S/D) regions 118 a and 118 b in the substrate 100. The S/D regions 118 a are formed in the first region 100A of the substrate 100 and are located at two opposite sides of the gate stacked structure which includes the interfacial layer 111 a, the high-k dielectric layer 112 a, the dummy poly gate electrode 113 a and the hard mask layer 114 a. The S/D regions 118 b are formed in the second region 100B of the substrate 100 and are located at two opposite sides of the gate stacked structure which includes the gate dielectric layer 110 b, the poly gate electrode 115 a and the hard mask layer 116 a. The source/drain regions 118 a and 118 b may be formed successively or simultaneously. The dopants for the source/drain regions 118 a, 118 b may be of opposite conductive type as that of the corresponding well regions 108 a, 108 b, respectively. For example, when the well region 108 a or 108 b is an n-type well, and the corresponding source/drain regions 108 a or 108 b may be doped with p-type dopants (e.g., boron or BF₂ ⁺). Similarly, when the well region 108 a or 108 b is a p-type well, and the corresponding source/drain regions 108 a or 108 b may be doped with n-type dopants (e.g., phosphorous or arsenic). In some embodiments, the dopant concentrations and/or the depths of the source/drain regions 108 a and the source/drain regions 108 b may be the same or different. In some embodiments, an annealing process may be further performed to anneal the source/drain regions 108 a and 108 b in the substrate 100 such that the dopant (or implanted ion) may diffuse. In some embodiments, the dummy poly gate electrode 113 a and the poly gate electrode 115 a are also doped during the one or more implantation processes of the S/D regions 118 a and 118 b.

In some embodiments, channels 120 a and 120 b are respectively defined in the substrate 100. The channel 120 a is located in the first region 100A of the substrate 100, underlies the interfacial layer 111 a, and extends from one of the S/D regions 118 a to the other of the S/D regions 118 a. The channel 120 b is located in the second region 100B of the substrate 100, underlies the gate dielectric layer 110 b, and extends from one of the S/D regions 118 b to the other of the S/D regions 118 b.

In some embodiments, a self-aligned silicide (salicide) process is performed to form metal silicide layers 119 a and 119 b respectively on the S/D regions 118 a and 118 b. In some embodiments, the metal silicide layers 119 a and 119 b include nickel silicide (NiSi), cobalt silicide (CoSi), titanium silicide (TiSi), tungsten silicide (WSi), molybdenum silicide (MoSi), platinum silicide (PtSi), palladium silicide (PdSi), CoSi, NiCoSi, NiPtSi, Ir, PtIrSi, ErSi, YbSi, PdSi, RhSi, or NbSi, or combinations thereof. In some embodiments, a metal layer (not shown) is formed over the substrate 100 to at least cover the S/D regions 118 a and 118 b. Thereafter, an annealing process is performed such that the metal layer is reacted with the S/D regions 118 a and 118 b, so as to form the metal silicide layers 119 a and 119 b. The unreacted metal layer is then removed.

Referring to FIG. 11 and FIG. 12, a photoresist material layer (not shown) is formed over the substrate 100 to cover the semiconductor structure shown in FIG. 11. The photoresist material layer may be formed by, for example, a spin coating process. Thereafter, the photoresist material layer is partially removed by, for example, an etching back process to form a photoresist layer PR exposing the hard mask layer 114 a and the hard mask layer 116 a. In some embodiments, upper portions of the spacers 117 a and 117 b are also exposed by the photoresist layer PR. In some embodiments, a top surface of the photoresist layer PR is lower than the top surfaces of the hard mask layer 114 a and the hard mask layer 116 a.

Referring to FIG. 12 and FIG. 13, the hard mask layer 114 a and the hard mask layer 116 a are removed, such that the top surface of the dummy poly gate electrode 113 a and the top surface of the poly gate electrode 115 a are exposed. In some embodiments, the hard mask layer 114 a and the hard mask layer 116 a are removed by an etching process using the photoresist layer PR as an etching mask. In some embodiments, portions of the spacers 117 a and 117 b are also removed. In some embodiments, topmost ends of the spacers 117 a are substantially levelled with the top surface of the dummy poly gate electrode 113 a, and/or topmost ends of the spacers 117 b are substantially levelled with the top surface of the poly gate electrode 115 a. In some alternative embodiments, topmost ends of the spacers 117 a are lower or higher than the top surface of the dummy poly gate electrode 113 a, and/or topmost ends of the spacers 117 b are lower or higher than the top surface of the poly gate electrode 115 a.

Referring to FIG. 13 and FIG. 14, the photoresist layer PR is then removed by, for example, a stripping process or an ashing process. As shown in FIG. 14, the interfacial layer 111 a, the high-k dielectric layer 112 a, the dummy poly gate electrode 113 a and the spacers 117 a constitute a dummy poly gate DG. The high-k dielectric layer 112 a is disposed on the interfacial layer 111 a. The dummy poly gate DG is disposed on the high-k dielectric layer 112 a. The spacers 117 a cover the sidewalls of the interfacial layer 111 a, the high-k dielectric layer 112 a and the dummy poly gate electrode 113 a. The interfacial layer 111 a and the high-k dielectric layer 112 a may be collectively referred to as a gate dielectric layer 110 c of the dummy poly gate DG.

The gate dielectric layer 110 b (e.g., gate oxide layer), the poly gate electrode 115 a and the spacers 117 b constitute a poly gate PG. The poly gate electrode 115 a is disposed on the gate dielectric layer 110 b. The spacers 117 b cover the sidewalls of the dielectric layer 110 b and the poly gate electrode 115 a. The thickness of the gate dielectric layer 110 b is larger than the thickness of the gate dielectric layer 110 c. It is noted that no high-k dielectric layer is sandwiched between the poly gate electrode 115 a and the gate dielectric layer 110 b (e.g., gate oxide layer), and the poly gate electrode 115 a is formed in contact with the gate dielectric layer 110 b. Therefore, the poly gate PG may not suffer fermi-level pinning issue caused by the worse interface between the poly gate electrode and the high-k dielectric layer.

Referring to FIG. 14 and FIG. 15, an etching stop material layer 121 is formed over the substrate 100 to cover the dummy poly gate DG, the poly gate PG, the S/D regions 118 a, 118 b, the metal silicide layers 119 a, 119 b and the isolation structures 106. In some embodiments, the etching stop material layer 121 is referred to as a contact etch stop layer (CESL). The etching stop material layer 121 may be formed by atomic layer deposition (ALD), CVD, plasma-enhanced CVD (PECVD), high density plasma CVD (HDPCVD), or other suitable methods. Subsequently, an interlayer dielectric material layer 122 is formed on the etching stop material layer 121. The interlayer dielectric material layer 122 may be formed by CVD, PECVD, HDPCVD, flowable CVD (FCVD), spin coating, or other suitable methods. The etching stop material layer 121 and the interlayer dielectric material layer 122 may be made of different materials. In some embodiments, the etching stop material layer 121 includes SiN, SiC, SiOC, SiON, SiCN, SiOCN, or the like, or combinations thereof. In some embodiments, the interlayer dielectric material layer 122 includes silicon oxide, carbon-containing oxide such as silicon oxycarbide (SiOC), silicate glass, tetraethylorthosilicate (TEOS) oxide, un-doped silicate glass, or doped silicon oxide such as borophosphosilicate glass (BPSG), fluorine-doped silica glass (FSG), phosphosilicate glass (PSG), boron doped silicon glass (BSG), combinations thereof and/or other suitable dielectric materials. In some embodiments, the interlayer dielectric material layer 122 may include low-k dielectric material with a dielectric constant lower than 4, extreme low-k (ELK) dielectric material with a dielectric constant lower than 2.5. In some embodiments, the low-k material includes a polymer based material, such as benzocyclobutene (BCB), FLARE®, or SILK®; or a silicon dioxide based material, such as hydrogen silsesquioxane (HSQ) or SiOF. The interlayer dielectric material layer 122 may be a single layer structure or a multi-layer structure.

Referring to FIG. 15 and FIG. 16, a planarization process is performed to remove portions of etching stop material layer 121 and the interlayer dielectric material layer 122 until the top surfaces of the dummy poly gate DG and the poly gate PG are exposed, so as to form an etching stop layer 121 a and an interlayer dielectric layer 122 a on the etching stop layer 121 a. The etching stop layer 121 a may cover top surfaces of the metal silicide layers 119 a, 119 b and the isolation structures 106 and sidewalls of the dummy poly gate DG and the poly gate PG. The interlayer dielectric layer 122 a may wrap around the dummy poly gate DG and the poly gate PG. In some embodiments, during the planarization process, upper portions of the dummy poly gate DG and/or the poly gate PG are also removed. In some embodiments, after the planarization process is performed, the top surfaces of the dummy poly gate DG and/or the poly gate PG may be substantially levelled with the top surface of the interlayer dielectric layer 122 a and the topmost end of the etching stop layer 121 a. The planarization process may include a chemical mechanical polishing (CMP) process.

During the planarization process of the etching stop material layer 121 and the interlayer dielectric material layer 122, the poly gate electrode 115 a of the poly gate PG may be polished under a polishing rate which is much less than those of the etching stop material layer 121 and the interlayer dielectric material layer 122. Therefore, the poly gate PG may not suffer dishing issue during the planarization process.

After the planarization process, a gate replacement process is performed to replace the dummy poly gate DG with a metal gate MG (shown in FIG. 19). The gate replacement process is described in accompany with FIGS. 17 through 19 in detail.

Referring to FIG. 17, a mask layer 123 may be formed over the second region 100B of the substrate 100 to cover the poly gate PG, and the top surface of the dummy poly gate DG may be exposed. In some embodiments, the mask layer 123 may include a dielectric material, such as silicon oxide, silicon nitride, or the like. The material of the mask layer 123 is merely for illustration and the disclosure is not limited thereto. Thereafter, the dummy poly gate electrode 113 a is removed by an etching process until the high-k dielectric layer 112 a is exposed, such that a trench TH is formed between the spacers 117 a.

Referring to FIG. 17 and FIG. 18, the mask layer 123 is removed and a metal gate material layer 124 is formed over the substrate 100 to fill the trench TH. In some embodiments, the metal gate material layer 124 may entirely cover the top surfaces of the interlayer dielectric layer 122 a and the poly gate PG and entirely fill the trench TH.

In some embodiments, the metal gate material layer 124 may include a work function layer (not individually illustrated) and a fill metal layer (not individually illustrated) on the work function metal layer. The work function metal layer may be an N-type work function metal layer or a P-type work function metal layer. In some embodiments, the N-type work function metal layer includes TiAl, TiAlN, or TaCN, conductive metal oxide, and/or a suitable material. In alternative embodiments, the P-type work function metal layer includes TiN, WN, TaN, conductive metal oxide, and/or a suitable material. The fill metal layer includes copper, aluminum, tungsten, or other suitable metallic materials. In some embodiments, the metal gate material layer 124 may further include a liner layer, an interface layer, a seed layer, an adhesion layer, a barrier layer, a combination thereof or the like. In some embodiments, the metal gate material layer 124 is formed by suitable processes such as ALD, CVD, PVD, plating process, or combinations thereof.

Referring to FIG. 18 and FIG. 19, a planarization process is performed to remove excess portion of the metal gate material layer 124 outside the trench TH to form a metal gate electrode 124 a in the trench TH. In some embodiments, after the planarization process is performed, the top surface of the metal gate electrode 124 a may be substantially levelled with the top surface of the interlayer dielectric layer 122 a, the topmost end of the etching stop layer 121 a, and the top surfaces of the spacers 117 a, and the top surface of the poly gate electrode 115 a may be substantially levelled with the top surface of the interlayer dielectric layer 122 a, the topmost end of the etching stop layer 121 a, and the top surfaces of the spacers 117 b. The planarization process may include a chemical mechanical polishing (CMP) process. As shown in FIG. 19, the interfacial layer 111 a, the high-k dielectric layer 112 a, the metal gate electrode 124 a and the spacers 117 a constitute the metal gate MG. The high-k dielectric layer 112 a is disposed on the interfacial layer 111 a. The metal gate electrode 124 a is disposed on the high-k dielectric layer 112 a. The spacer 117 a covers the sidewalls of the interfacial layer 111 a, the high-k dielectric layer 112 a and the metal gate electrode 124 a.

During the planarization process of the metal gate material layer 124, the poly gate electrode 115 a of the poly gate PG may be polished under a polishing rate which is much less than that of the metal gate material layer 124. Therefore, the poly gate PG may not suffer dishing issue during the planarization process.

It is noted that, in some embodiments, the mask layer 123 is removed before the metal gate material layer 124 is formed, which is merely for illustration, and the disclosure is not limited thereto. In alternative embodiments, the mask layer 123 is removed during the afore-mentioned planarization process of the metal gate material layer 124.

Referring to FIG. 19 and FIG. 20, a dielectric layer 125 is formed over the first region 100A of the substrate 100 to cover the metal gate MG, and the top surface of the poly gate PG may be exposed. In some embodiments, the material of the dielectric layer 125 may be similar to that of the interlayer dielectric layer 122 a. Thereafter, a self-aligned silicide (salicide) process is performed to form a metal silicide layer 126 on the poly gate PG. In some embodiments, the metal silicide layer 126 includes nickel silicide (NiSi), cobalt silicide (CoSi), titanium silicide (TiSi), tungsten silicide (WSi), molybdenum silicide (MoSi), platinum silicide (PtSi), palladium silicide (PdSi), CoSi, NiCoSi, NiPtSi, Ir, PtIrSi, ErSi, YbSi, PdSi, RhSi, or NbSi, or combinations thereof. In some embodiments, a metal layer (not shown) is formed over the substrate 100 to at least cover the poly gate electrode 115 a. Thereafter, an annealing process is performed such that the metal layer is reacted with the poly gate electrode 115 a, so as to form the metal silicide layers 126. The unreacted metal layer is then removed.

Referring to FIG. 20 and FIG. 21, an inter-layer dielectric layer 127 is formed over the substrate 100 to cover the dielectric layer 125 and the metal silicide layer 126. In some embodiments, the material of the inter-layer dielectric layer 127 may be similar to that of the interlayer dielectric layer 122 a. In some embodiments, the inter-layer dielectric layer 127 and the dielectric layer 125 are made of the same material. In alternative embodiments, the inter-layer dielectric layer 127 and the dielectric layer 125 are made of different materials. In this case, the dielectric layer 125 may be removed before the inter-layer dielectric layer 127 is formed. After the inter-layer dielectric layer 127 is formed, the inter-layer dielectric layer 127, the dielectric layer 125, the interlayer dielectric layer 122 a and the etching stop layer 121 a are patterned to form a plurality of through openings OP penetrating through these layers. Some of the through openings OP may expose the respective metal silicide layers 119 a or 119 b. Some of the through openings OP may expose the metal gate MG or the poly gate PG (not shown in the cross-sectional view of FIG. 21).

Referring to FIG. 21 and FIG. 22, a contact conductive material (not shown) is filled into the through openings OP and covers the inter-layer dielectric layer 127. A planarization process is then performed to remove excess contact conductive material outside the through openings OP, such that a plurality of source/drain contacts 128 a and 128 b and gate contacts (not shown in the cross-sectional view of FIG. 22) are formed in the through openings OP. The source/drain contacts 128 a are formed on the metal silicide layer 119 a to electrically connect to the S/D regions 118 a. The source/drain contacts 128 b are formed on the metal silicide layer 119 b to electrically connect to the S/D regions 118 b. The gate contacts are formed to electrically connect to the metal gate MG or the poly gate PG. In some embodiments, each of the source/drain contacts 128 a, 128 b and the gate contacts includes a barrier layer (not individually illustrated) and a conductive layer (not individually illustrated) on the barrier layer. The barrier layer may surround sidewalls and/or bottom surface of the conductive layer. The barrier layer may include titanium, tantalum, titanium nitride, tantalum nitride, manganese nitride or combinations thereof. The conductive layer may include metal, such as tungsten (W), copper (Cu), Ru, Ir, Ni, Os, Rh, Al, Mo, Co, alloys thereof, combinations thereof or any metallic material with suitable resistance and gap-fill capability. In some embodiments, the top surfaces of the source/drain contacts 128 a, 128 b and the gate contacts are substantially levelled with the top surface of the inter-layer dielectric layer 127. It is understood that the semiconductor device of the disclosure may be formed by CMOS technology processing, and thus some processes are not described in detail herein.

As shown in FIG. 22, a semiconductor device 10 including a first transistor TR1 and a second transistor TR2 is formed. The first transistor TR1 is disposed in/on the first region 100A of the substrate 100 and includes the metal gate MG, the S/D regions 118 a and the channel 120 a. The second transistor TR2 is disposed in/on the second region 100B of the substrate 100 and includes the poly gate PG, the S/D regions 118 b and the channel 120 b. The metal gate MG is located on the first region 100A of the substrate 100. The S/D regions 118 a are located in the first region 100A of the substrate 100 and at opposite sides of the metal gate MG. The channel 120 a is located in the first region 100A of the substrate 100 and underlies the metal gate MG. The poly gate PG is located on the second region 100B of the substrate 100. The S/D regions 118 b are located in the second region 100B of the substrate 100 and at opposite sides of the poly gate PG. The channel 120 b is located in the second region 100B of the substrate 100 and underlies the poly gate PG. An aspect ratio of the poly gate PG is less than that of the metal gate MG. A gate area of the poly gate PG is greater than that of the metal gate MG. A channel length of the channel 120 b is greater than that of the channel 120 a. For example, the gate area of the poly gate PG may be greater than about 2 μm², such as about 5 μm² or about 10 μm². The gate area of the metal gate MG may be less than or equal to about 2 μm² or about 1 μm². The channel length of the channel 120 b may be greater than about 0.1 μm, or other suitable values. The channel length of the channel 120 a may be less than or equal to about 0.05 μm, or other suitable values.

In some embodiments, the first transistor TR1 with smaller gate area (or shorter channel length) may serve as a core device configured to aid in core functions for the IC. For example, the first transistor TR1 and other core devices (not shown) may collectively implement core circuitry for the IC. In some embodiments, the second transistor TR2 with larger gate area (or longer channel length) and thick gate oxide layer may serve as a high-voltage device configured to operate at a high operation voltage relative to the core device. The high voltages may, for example, range from about 20 to about 50 volts, about 10 to about 100 volts, about 30 to about 70 volts, or some other suitable high voltages.

Although not illustrated, the semiconductor device 10 may further include a third transistor which serves as an I/O device disposed in/on a third region of the substrate 100. A gate area (or channel length) of the I/O device may be greater than that of the first transistor TR1, and less than that of the second transistor TR2. Materials and forming method of the I/O device may be similar to those of the first transistor TR1 expect that the metal gate of the I/O device includes a gate oxide layer instead of an interfacial layer. That is, the gate dielectric layer of the I/O device includes the gate oxide layer and a high-k dielectric layer on the gate oxide layer. Materials and forming method of the gate oxide layer of the I/O device may be similar to those of the gate dielectric layer 110 b of the second transistor TR2, so the detailed descriptions are not repeated for the sake of brevity.

In view of the above, in some embodiments of the disclosure, since the poly gate serves as the gate structure having larger gate area, the dishing issue is avoided due to the high selectivity of the poly gate electrode during the planarization process. Therefore, the reliability and performance of the device are accordingly improved. Furthermore, the manufacturing process of the semiconductor device is compatible to HKMG process.

In accordance with some embodiments of the disclosure, a semiconductor device includes a substrate, a metal gate and a poly gate. The substrate includes a first region and a second region. The metal gate is disposed on the first region of the substrate. The poly gate is disposed on the second region of the substrate. A gate area of the poly gate is greater than that of the metal gate.

In accordance with some embodiments of the disclosure, a semiconductor device includes a substrate, a metal gate, a first channel, a poly gate and a second channel. The substrate includes a first region and a second region. The metal gate is disposed on the first region of the substrate. The first channel is located in the first region of the substrate and underlies the metal gate. The poly gate is disposed on the second region of the substrate. The second channel is located in the second region of the substrate and underlies the poly gate. A channel length of the second channel is greater than that of the first channel.

In accordance with some embodiments of the disclosure, a method of forming a semiconductor device includes the following steps. A substrate including a first region and a second region is provided. A dummy poly gate is formed on the first region of the substrate. A poly gate is formed on the second region of the substrate. The dummy poly gate is replaced with a metal gate. A gate area of the poly gate is greater than that of the metal gate.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A semiconductor device, comprising: a substrate comprising a first region and a second region; a metal gate disposed on the first region of the substrate; and a poly gate disposed on the second region of the substrate, wherein a gate area of the poly gate is greater than that of the metal gate.
 2. The semiconductor device as claimed in claim 1, wherein the poly gate comprises a gate oxide layer and a poly gate electrode on the gate oxide layer.
 3. The semiconductor device as claimed in claim 2, wherein the poly gate electrode is in contact with the gate oxide layer.
 4. The semiconductor device as claimed in claim 1, wherein the metal gate comprises an interfacial layer, a high-k dielectric layer on the interfacial layer and a metal gate electrode on the high-k dielectric layer.
 5. The semiconductor device as claimed in claim 1, further comprising a metal silicide layer on the poly gate.
 6. The semiconductor device as claimed in claim 1, wherein an aspect ratio of the poly gate is less than that of the metal gate.
 7. A semiconductor device, comprising: a substrate comprising a first region and a second region; a metal gate disposed on the first region of the substrate; and a first channel located in the first region of the substrate and underlying the metal gate; a poly gate disposed on the second region of the substrate; and a second channel located in the second region of the substrate and underlying the poly gate, wherein a channel length of the second channel is greater than that of the first channel.
 8. The semiconductor device as claimed in claim 7, wherein the poly gate comprises: a gate oxide layer; a poly gate electrode on the gate oxide layer; and spacers on sidewalls of the gate oxide layer and the poly gate electrode.
 9. The semiconductor device as claimed in claim 8, wherein the poly gate electrode is in contact with the gate oxide layer.
 10. The semiconductor device as claimed in claim 7, wherein the metal gate comprises: an interfacial layer; a high-k dielectric layer on the interfacial layer; a metal gate electrode on the high-k dielectric layer; and spacers on sidewalls of the interfacial layer, the high-k dielectric layer and the metal gate electrode.
 11. The semiconductor device as claimed in claim 7, further comprising a metal silicide layer on the poly gate.
 12. A method of forming a semiconductor device, comprising: providing a substrate comprising a first region and a second region; forming a dummy poly gate on the first region of the substrate; forming a poly gate on the second region of the substrate; and replacing the dummy poly gate with a metal gate, wherein a gate area of the poly gate is greater than that of the metal gate.
 13. The method as claimed in claim 12, wherein forming the dummy poly gate on the first region of the substrate comprises: forming an interfacial layer, a high-k dielectric layer and a dummy poly gate electrode stacked in sequence over the first region of the substrate.
 14. The method as claimed in claim 13, wherein replacing the dummy poly gate with the metal gate comprises: removing the dummy poly gate electrode; and forming a metal gate electrode on the high-k dielectric layer.
 15. The method as claimed in claim 14, wherein replacing the dummy poly gate with the metal gate further comprises: forming a mask layer over the second region of the substrate to cover the poly gate prior to removing the dummy poly gate electrode; and removing the mask layer after the dummy poly gate electrode is removed.
 16. The method as claimed in claim 13, wherein forming the poly gate on the second region of the substrate comprises: forming a gate oxide layer and a poly gate electrode over the second region of the substrate, wherein the poly gate electrode is formed in contact with the gate oxide layer.
 17. The method as claimed in claim 16, wherein the dummy poly gate electrode of the dummy poly gate is formed before or after the poly gate electrode of the poly gate is formed.
 18. The method as claimed in claim 12, further comprising: forming a metal silicide layer on the poly gate.
 19. The method as claimed in claim 18, further comprising: forming a dielectric layer over the first region of the substrate to cover the metal gate prior to forming the metal silicide layer on the poly gate.
 20. The method as claimed in claim 19, further comprising: forming an inter-layer dielectric layer over the substrate to cover the dielectric layer and the metal silicide layer. 